The present invention relates to rail fixings. It is more particularly concerned with rail fixings that exhibit advantageous noise characteristics.
The noise emitted by moving rail vehicles is a major limitation on their use, in that it will limit the ability of operators to install new lines in populated areas, and will limit speeds and traffic volumes on existing lines. The noise tends to be dominated by rolling noise from the wheel/rail interface, which is caused partly by vibration of the wheels and partly by vibration of the track.
It is not possible to select alternative materials, etc, for these elements since they are subject to very high transient loads during use, and must withstand these. Materials which would be able to absorb vibration and hence reduce noise would be unable to survive in use for any appreciable time. Resilient rail fastenings have been employed to reduce track forces and thereby reduce component damage and structure-borne noise. However, they have an adverse effect on track noise as they tend to reduce the attenuation of rail vibration.
The present invention seeks to provide a means for reducing the track noise emitted by a rail system. It therefore provides a damper for a rail, comprising at least one deformable material attachable to a surface of the rail and incorporating a plurality of elongate resonant members, the resonant members being of a stiff material as compared to the deformable material and being sized to form a resonant system with at least two resonances in the frequency range where rail vibration is to be reduced.
It is preferred if the resonant members are of different profile, as this provides an easy way of tuning to two different frequencies. However, this can still be achieved with identical profiles. They are suitably embedded in the deformable material, as this both ensures adequate vibrational transfer from the rail to the resonant members and also provides environmental protection. They are ideally more dense than the resilient material. They are suitably of steel or other dense material.
The deformable member is preferably visco-elastic, for example rubber or a rubber-like material. This may be preformed and glued to the rail, or it can be cured in place on the rail.
It is strongly preferred that the damper is positioned on the rail so as to cover the junction between the web and the foot of the rail. This has been found to be exceptionally advantageous in terms of the amount of damping needed to achieve adequate noise reduction. At this position, a damper with at least two resonant frequencies according to the invention can reduce significantly the noise level of the rail. One resonant member can be a elongate angled section, the angle preferably matching the angle between external surfaces of the head and foot. Another resonant member can be a solid elongate block, the external faces adjacent the web and foot being angled to match. Further resonant members can be employed as necessary.
The damper will be easier to manufacture and easier to apply to existing rail if the resonant members are discontinuous within the deformable material. Ideally, the discontinuities in the plurality of resonant members will coincide. It is also possible to apply the damper in discrete sections, leaving gaps (for example) for rail fasteners. However, a continuous length of damper is preferred.
It is preferable for there to be a pair of such dampers, one either side of the rail.
An embodiment of the present invention will now be described, by way of example, with reference to the accompanying Figures;